Monday, December 30, 2013

Amplifier Raised on Brass Feet from Mapleshade

Raising my Aragon 8008 BB on a quad set of custom order brass Mapleshade Threaded Thick Carpet Heavyfeet has lowered the operating temperature of the amplifier considerably, and improved the sound slightly. The feet allow the amplifier to sit directly above the carpet without a wood platform underneath. The lack of a makeshift wood platform (a repurposed shelf from an audio rack) has also cleaned up the appearance considerably, created more foot room, and for their part the brass feet look very nice too.

I was very surprised from the large drop in heatsink temperature. In fact, one of the many excuses for not putting these feet on the amplifier sooner (I actually bought them about two years ago) was that I feared that while the amplifier might sit slightly higher above the visible surface of the carpet than it previously sat on the wood shelf, the (plain pile) texture of the carpet would still impede airflow more than the wood, and the last thing I would want for the already too hot Aragon amplifier (which used to idle at about 133 degrees F at the top of the heatsinks) would be for it to run hotter. Of course the actual feet that I purchased (which required a custom order because of the stud size of the amplifier) were the carpet-ready variety, with a 3/4 slender spike which pushes through the carpeting. But I still worried that it wasn't enough. The total foot size is 2 1/4 inch, leaving at least 1 1/2 inch above the carpeting.

As it turned out, not only were my fears unwarranted, I now regret that I did not put these feet on the amplifier at the very first moment I could to keep it cooler. The heatsink temperature at idle has now lowered to about 117 degrees F, a 16 degree drop in temperature, which might mean a twofold or greater increase in longevity, or technically MTBF (mean time between failure). For quite awhile, I even ran the amplifier night and day (mainly because it was more convenient, and I figured that it might sound better, but the truth is the idle bias on this amplifier is so high it probably makes little difference, it pops right up to full idle current within a minute of being turned on, and for longevity reasons it's desirable not to keep the amplifier hot so much).

As to the sound, it seems a bit clearer and cleaner, and sounds slightly more relaxed as well. No minuses whatever.

Since my listening position is now just a couple of feet back from the speaker plane, the extra foot room is appreciated also, and this makes the new listening position much more guest-friendly for taller people than me, which most people are.

Given that I now have (and have had for about two years) a great infrared thermometer to verify before and after temperatures, putting the feet was about as easy as an audio modification can get. Disconnect amplifier, turn on side, remove old feet, then add new feet. The old "feet" were three layers of adhesive felt sliders. The amplifier came with one set of adhesive feet like this, which were only about 1/4 inch thick. Once I became aware of how hot the amplifier was running, after a few more months of inaction, I added two more adhesive felt feet on top (or underneath, actually) the existing feet. All this time I had the amplifier's feet resting on a solid wood board. Strangely, i don't recall that adding the extra felt feet made any difference in the operating temperature, though I do remember seeing idle temperatures as high as 136 degrees previously, so I'll give the benefit of the doubt to a 3 degree improvement. (Given changes in ambient temperature, HVAC operation, and so on, all these measured differences should be taken with a grain of salt anyway. But I measured the 16 degrees of improvement with the Mapleshade feet on the same afternoon/evening, and I've been seeing the 133 degree idle temperatures for a fairly long time), so while I'm uncertain about how much if any change was made by trebling the felt feet, the big brass feet have made a large and clearly measurable different in amplifier temperature.

Although this was fast, I chose to do some extra stuff that other people might not have bothered with. Rather than simply assuming all was OK after screwing on the feet, I took the small cover off the top of the Aragon to check the wiring on the right side. Those feet are right underneath the active guts of one channel. I could see into the area just a bit using a flashlight, but not well enough, so I removed the cover after I'd set the amplifier back down. (One problem with this is that you can't screw the feet on and have the covers removed at the same time.) Toward the back of the amplifier there was no interference with the new screw stud. But in the front there was a bundle of wires running through. Most of that bundle simply got pushed up by the stud, leaving just one insulated wire running a bit closer to the nearby power transistor than desirable.

I first put a nylon wire tie onto the screw stud itself. That meant that no wire was directly contacting the screw. But then it was clear that no matter how I wrapped the wires, the straggler still turned rather close to a power transistor. So I then put a second wire tie around the entire bundle of wires, just above where the first screw tie wraps around the screw. The effect of that is to keep the straggler wire in place with the rest of the bundle, AND to lock the whole bundle in place, just slightly above the screw and separated by nylon and air for thermal insulation. After examining that for awhile, I put the cover back on. I didn't remove the larger cover on the right side of the amp because there is no circuitry where those screw holes are, or any power transistors, though the screw studs could have pushed a wire out of the way, it would be otherwise harmless.

As it turned out, only one of the feet allowed the stud to screw nearly all the way in. On the other feet, the screws would turn in leaving about 3/8" above the foot. For most of the feet, I screwed the stud in first as far as it would go, then I screwed the foot and screw assembly onto the amplifier. In every case this made it impossible to feel the screw starting position by turning the screw backwards (as I usually do) so I had to simply screw the screws on clockwise as most people do, and it wasn't easy to get the screws lined up. For the other foot, I screwed the screw in not as far as it would go, but to the same distance as the others.

Had I really examined the amp first, I might have used the special foot (which allows the screw to go nearly all the way in) just at that location where I was forced to use wire ties, that way I could have avoided the wire ties. But it was that sort of endless thinking that kept me from doing this otherwise fairly simple but very important upgrade.